Recruiting diverse populations to clinical trials helps ensure that study results are generalizable to the population at large. The primary goal of this study is to identify and describe characteristics of clinical trials that have explicit inclusion o exclusion criteria related to minority race, ethnicity, or English fluency. While explicit exclusio of African Americans from some recent clinical trials has received attention from advocacy organizations, there has not been much research documenting the degree to which such exclusions continue to be widespread. Also, little is known about the characteristics of trials tha are associated with such exclusionary eligibility criteria. We hypothesize that clinical trials wit sponsoring institutions located in more racially and ethnically diverse areas are more likely to have racial, ethnic, or English fluency-related eligibility criteria. We propose using data from th ClinicalTrials.gov database for this project. We will link the ClinicalTrials.gov data to United States Census and American Community Survey data to obtain information on the areas surrounding institutions that sponsor these trials. We will also record justifications given for exclusionary language. Our preliminary findings suggest that investigator desires to increase the internal validity of their trials is a primary motivator for excluding minorities. Indeed, there isan inherent tradeoff in trying to ensure both the internal and external validity of clinical trials. Te internal validity refers to the ability of a study to correctly determine whether an intervention i efficacious, while external validity refers to the ability of a study's findings to be replicated i a more general population. Increasing a trial's external validity can increase heterogeneity in effect estimators which reduces the internal validity of the trial. This R03 project will document the prevalence of racial, ethnic, and English language exclusions in clinical trials accruing in th United States. This study will also provide insight into the types of studies that are likely to hae exclusionary language. Such information can be useful in identifying the types of trials at high risk of having exclusionary language. Also, future work could investigate whether some of the variables associated with exclusionary eligibility criteria and identified over the course of this project might be used to develop interventions that could reduce explicit exclusionary criteria.